Display screen or portion thereof with a graphical user interface



FIG. 1 is a front view of a display screen or portion thereof with a graphical user interface showing a first image of the claimed design.

FIG. 2 is a second image thereof; and,

FIG. 3 is a third image thereof.

The broken line showing of a device is included for the purpose of illustrating environmental structure and forms no part of the claimed design. The broken line showing of text is included for the purpose of illustrating portions of the article and forms no part of the claimed design. The subject matter shown in FIGS. 1-3 includes a process or period in which an image changes into another image. This process or period forms no part of the claimed design. 

CLAIM The ornamental design for a display screen or portion thereof with a graphical user interface, as shown and described. 